California's Native Plant Species in Peril from Global Warming

Two-thirds of California’s native plants could suffer more than an 80% reduction in geographic range by the end of the century, according to a new study.

Climate scientist Katharine Hayhoe, MS, who contributed to the Nobel-Prize–winning United Nations Intergovernmental Panel on Climate Change, prepared high-resolution projections for California’s future climate for an ecological study by researchers at the University of California, Berkeley, and Duke University. Their results were published Wednesday in the journal PLoS ONE.

The study tracked 5,500 native California plants, including the renowned Coast Redwood tree, and predicted how changing climate conditions could affect their dispersal throughout the region. Hayhoe says climate change will likely push these plants farther north or to higher elevations, in many cases reducing the range size or even causing extinctions.

“The bad news is that the climate change we may experience in the future could have this kind of drastic impact on California’s native plant species,” she says. “Many species may have to move to cooler areas in order to survive. In some of these cases, for example, when a plant grows near the top of a mountain, there’s nowhere to go.

“But there is some good news,” she continues. “We can use this information to find out where we can set aside land for conservation purposes now, so these plants can be preserved.”

Because endemic species—native species not found outside the state—make up nearly half of all California’s native plants, a changing climate will have a major impact on the state’s unparalleled plant diversity, the researchers warn.

“Our study projects that climate change will profoundly impact the future of the native flora in California,” says David Ackerly, PhD, a professor of integrative biology at UC Berkeley. “The magnitude and speed of climate change today is greater than during past glacial periods, and plants are in danger of getting killed off before they can adjust their distributions to keep pace.”

The researchers caution that their study can’t reliably predict the fate of specific species. But the trend is clear: The researchers believe that in response to rising temperatures and altered rainfall, many plants could move northward and toward the coast, following the shifts in their preferred climate. Others, primarily in the southern part of the state and Baja California, may move up mountains into cool but highly vulnerable “refugia” (places where large numbers of plants hit hardest by climate change are projected to survive).

Coast Redwoods may range farther north, for example, while California oaks could disappear from central California in favor of cooler weather in the Klamath Mountains along the California-Oregon border.

Many plants may no longer be able to survive in the northern Sierra Nevada or in the Los Angeles basin, while plants of northern Baja California will migrate north into the San Diego mountains. The Central Valley will become preferred habitat for plants of the Sonoran desert.

“Across the flora, there will be winners and losers,” says first author Scott Loarie, a doctoral candidate at Duke University’s Nicholas School for the Environment. “In nearly every scenario we explored, biodiversity suffers—especially if the flora can’t disperse fast enough to keep pace with climate change.”

The authors identified several “climate-change refugia” scattered around the state. Many are in the foothills of coastal mountains, such as the Santa Lucia Mountains along California’s Central Coast, the Transverse Ranges separating the Central Valley from Los Angeles, and the San Gabriel Mountains east of L.A. Many face pressure from encroaching development.

“There’s a real potential for sheltering a large portion of the flora in these refugia if they are kept wild and if plants can reach them in time,” Loarie says.

The authors argue it’s not too early to prepare for this eventuality by protecting corridors through which plants can move to such refugia, and maybe even assisting plants in reestablishing themselves in new regions.

“Part of me can’t believe that California’s flora will collapse over a period of 100 years,” Dr. Ackerly says. “It’s hard to comprehend the potential impacts of climate change. We haven’t seen such drastic changes in the last 200 years of human history, since we have been cataloguing species.”

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